For some applications, shells are formed around molds to achieve a negative of the mold. The shells are then removed from the molds to be further used for various applications. One example application in which a shell is formed around a mold and then later used is corrective dentistry or orthodontic treatment. In such an application, the mold may be a positive mold of a dental arch for a patient and the shell may be an aligner to be used for aligning one or more teeth of the patient. When attachments are used, the mold may also include features associated with planned orthodontic attachments and virtual fillers.
Molds may be formed using casting or rapid prototyping equipment. For example, 3D printers may manufacture the molds using additive manufacturing techniques (e.g., stereolithography) or subtractive manufacturing techniques (e.g., milling). The aligners may then be formed over the molds using thermoforming equipment. Once the aligner is formed, it may be manually or automatically trimmed. In some instances, a computer controlled 4-axis or 5-axis trimming machine (e.g., a laser trimming machine or a mill) is used to trim the aligner along a cutline. The trimming machine uses electronic data that identifies the cutline to trim the aligner. Thereafter, the aligner may be removed from the mold and delivered to the patient. While much of this process has been automated, further improvements may be had.